Variable-speed irrigation system

ABSTRACT

An irrigation system is disclosed that is configured to maintain a near straight alignment. In an implementation, an irrigation system includes multiple interconnected spans which are supported by multiple tower structures. Each tower structure includes a variable-speed drive unit for selectively driving a tower structure at a selected speed. The irrigation system also includes multiple sensors that are each associated with a corresponding span to determine an alignment of the corresponding span with respect to adjacent spans. Each of the sensors is in communication with a corresponding variable-drive control unit. Each of the variable-drive control units are configured to control the selected speed of a corresponding variable-speed drive unit to maintain the interconnected spans in a substantially linear orientation with respect to adjacent ones of the plurality of interconnected spans along a generally longitudinally oriented axis (e.g., maintain alignment of the spans with respect to each other).

BACKGROUND

Modern day agriculture has become increasingly efficient in the pastcentury and this trend must continue in order to produce a sufficientfood supply for the increasing world population. A notable advancementin agricultural production was the introduction of mechanized irrigationsystems, such as the center pivot and the linear move irrigationsystems. These irrigation systems make it possible to irrigate entirefields, and reduce a crop yield's vulnerability to extreme weatherconditions. The ability to monitor and to control the amount of waterand/or nutrients (applicants) applied to an agricultural field hasincreased the amount of farmable acres in the world and increases thelikelihood of a profitable crop yield. These irrigation systemstypically include a control device configured to furnish a userinterface allowing the operator to monitor and control one or morefunctions or operations of the irrigation system.

SUMMARY

An irrigation system is disclosed that is configured to maintain a nearstraight (e.g., an at least zero degree (0°)) alignment. In animplementation, an irrigation system includes multiple interconnectedspans which are supported by multiple tower structures. Each towerstructure includes a variable-speed drive unit for selectively driving atower structure at a selected speed. In a specific implementation, thevariable-speed drive units may be switched reluctance motors. Theirrigation system also includes multiple sensors that are eachassociated with a corresponding span to determine an alignment of thecorresponding span with respect to adjacent spans. Each of the sensorsis in communication with a corresponding variable-drive control unit.Each of the variable-drive control units are configured to control theselected speed of a corresponding variable-speed drive unit to maintainthe interconnected spans in a substantially linear orientation withrespect to adjacent ones of the plurality of interconnected spans alonga generally longitudinally oriented axis (e.g., maintain alignment ofthe spans with respect to each other). In a specific implementation, thevariable-drive control units may be in direct communication with thecorresponding sensor.

This Summary is provided solely to introduce subject matter that isfully described in the Detailed Description and Drawings. Accordingly,the Summary should not be considered to describe essential features norbe used to determine scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different instances in thedescription and the figures may indicate similar or identical items.

FIG. 1A is an isometric diagrammatic perspective view of an irrigationsystem in accordance with an example implementation of the presentdisclosure.

FIG. 1B is a block diagram illustrating a control device of theirrigation system shown in FIG. 1A in accordance with an exampleimplementation of the present disclosure.

FIG. 1C is a block diagram illustrating a sensor in electroniccommunication with a variable-drive control unit, wherein the variablecontrol device is configured to control the selected speed of avariable-drive unit based upon an alignment of corresponding adjacentspans as determined by the sensor.

FIG. 1D is a block diagram illustrating an example implementation of avariable-drive control unit that is configured to control avariable-drive unit, wherein the variable-drive control unit includes aprocessor, a memory, and a communication module configured tocommunicate with a sensor and the variable-drive unit.

DETAILED DESCRIPTION Overview

Most irrigation systems, such as center pivot irrigation systems,include drive units (motors) located on the drive towers to propel theirrigation system. Many of these rely on fixed rate motors due to theirrelative simplicity and robustness. However, such systems can onlyadjust the relative alignment of various span portions by alternativelystarting and stopping the drives. This results in drive towers coming toa complete stop and then requiring a large impulse of power to start thetower again. The starting and stopping places undue stress on variouscomponents of the irrigation system, which can accelerate wear andincrease maintenance costs. The irregular motion can also cause unevenapplication of irrigation water and/or chemicals to the field. Thisresults in waste of both water and chemicals. The irregular motion canalso cause errors in alignment or in determining the position of the endof the machine. This can result in errors in operations based onposition.

Accordingly, an irrigation system is disclosed that is configured tomaintain a near straight (e.g., an at least zero degree (0°)) alignment.In an implementation, an irrigation system includes multipleinterconnected spans which are supported by multiple tower structures.Each tower structure includes a variable-speed drive unit forselectively driving a tower structure at a selected speed. Theirrigation system also includes multiple sensors that are eachassociated with a corresponding span to determine an alignment of thecorresponding span with respect to adjacent spans. Each of the sensorsis in communication with a corresponding variable-drive control unit.Each of the variable-drive control units are configured to control theselected speed of a corresponding variable-speed drive unit to maintainthe interconnected spans in a substantially linear orientation withrespect to adjacent ones of the plurality of interconnected spans alonga generally longitudinally oriented axis (e.g., maintain alignment ofthe spans with respect to each other).

Example Implementations

FIG. 1A illustrates a self-propelled (e.g., mechanized) irrigationsystem (assembly) 100 in accordance with example implementations of thepresent disclosure. Examples of self-propelled irrigation systemsinclude a center pivot irrigation system, a linear move irrigationsystem, or the like. FIG. 1A illustrates an embodiment of the presentdisclosure where the irrigation system 100 is a center pivot irrigationsystem. However, it is contemplated that the present disclosure may beimplemented in other self-propelled irrigation systems (e.g., linearmove irrigation systems). As shown, the system 100 includes a centerpivot structure 102, a main section assembly 104 (irrigation sectionassembly) coupled (e.g., connected) to the center pivot structure 102.The center pivot structure 102 has access to a well, a water repository(e.g., water tank), or other fluid source, to furnish water to theirrigation system 100. For instance, the well may be located under thecenter pivot structure 102. In another instance, the well may be inclose proximity to the cultivation area (e.g., field). The fluid sourcemay be coupled to a repository or other source of agricultural productsto inject fertilizers, pesticides, and/or other chemicals into thefluids to create an applicant for application during irrigation. Thus,the applicant may be water, fertilizer, herbicide, pesticide,combinations thereof, or the like. The irrigation system 100 may becoupled to a fluid displacement device (e.g., a pump assembly)configured to furnish applicant throughout the irrigation system 100.For example, the fluid displacement device may assist in displacingfluid from the fluid source (e.g., well, water repository, etc.) to theconduit portions of the irrigation system which are described herein.The center pivot structure 102 can be fixed or can be towable such thatan operator can move the irrigation system 100 from one field toanother. In an implementation, the center pivot structure 102 maycomprise a frame assembly (e.g., galvanized steel frame assembly, and soforth).

The main section assembly 104 includes a number of interconnected spans106, 108, 109 (e.g., irrigation spans) supported by one or more towerstructures 110, 111 (intermediate tower structures) and an end towerstructure 112. The tower structures 110, 111, 112 may be any towerconfiguration known in the art to adequately support the conduits (e.g.,water pipe sections) described herein. It is understood that the sectionassembly 104 may include any number of spans and tower structures.

The tower structures 110, 111 and the end tower structure 112 eachinclude wheels 114, 116, to assist in traversing the irrigation system100 (e.g., allowing the main section assembly 104 to pivot) about acultivation area (e.g., field). In an implementation, the wheels 114,116 may be driven by a suitable variable-drive unit 118 (e.g., drivemotor), or the like, to assist in traversing the system 100 about thespecified area. For example, each tower structure 110 may include adrive unit 118 to propel the respective tower structure 110, 111, 112(and the irrigation system 100) through the cultivation area. In one ormore implementations, the drive units 118 comprise variable-speed motorsthat are configured to selectively drive a tower structure at a selectedspeed. For example, the drive units 118 may comprise electric switchedreluctance motors configured to drive the irrigation system 100 in aforward direction or a reverse direction. Typically, the alignmentbetween each span 106, 108, 109 (e.g., machine alignment) of theirrigation system 100 is maintained by a suitable mechanical linkage ateach drive unit span joint. The drive unit span joint is configured as apotentiometer, or other sensor, that serves to accelerate or deceleratethe respective drive unit 118 (switched reluctance motors, which aredescribed in greater detail below) to at least substantially keep therespective span 106, 108, 109 in alignment with the other irrigationspan. Alignment may be defined as each span 106, 108, 109 being alignedwith one or more adjacent spans along a generally linear longitudinalaxis (e.g., defined with respect to a generally horizontal surface, suchas the ground).

As shown in FIG. 1A, each span 106, 108 includes conduits 120, 121, 122(e.g., pipes) that are configured to carry (e.g., transport, provide,and so forth) liquid (e.g., applicant) along the length of the system100 to one or more applicant dispersal assemblies that are configured toirrigate the cultivation area. Each conduit 120, 121, 122 may be coupledto one another to allow fluid communication between each conduit. In animplementation, the conduits 120, 121, 122 may be supported bytruss-type framework structures 124, 125, 126. Thus, the main fluiddisplacement device may be configured to displace applicant through theconduits 120, 121, 122. As shown in FIG. 1A, the irrigation system 100also includes a cantilevered boom structure 128 that extends outwardlyfrom the end tower structure 112. In one or more implementations, thecantilevered boom 128 includes an end gun 129 (e.g., end gun 129 ismounted to the cantilevered boom 128). The end gun 129 may be a suitablepressure sprayer configured to be activated at the corners of a field,or other designated areas, to increase the amount of land that can beirrigated.

As shown in FIGS. 1A and 1B, the irrigation system 100 includes acontrol device 130 (e.g., control panel) that is in electroniccommunication with one or more components of the system 100. Forexample, the control device 130 may be in electronic communication withone or more tower boxes mounted at one or more tower structures 110,111, 112, and a position sensor 132 utilized to determine an approximateposition of the irrigation system (e.g., determining the approximateposition of the end tower structure 112 within the cultivation area withrespect to the center pivot structure 102). In an implementation, theposition sensor 132 may be a GPS sensor (e.g., GPS receiver), or thelike, mounted to the end tower structure 112 configured to transmitsignals representing the position of the end tower structure to thecontrol device 130. As described herein, the control device 130 isconfigured to determine the radial position of the main section assembly104 with respect to the center pivot structure 102. In anotherimplementation, the position sensor 132 may be an angle sensor 133configured to facilitate determination of the rotational position of themain section assembly 104. The angle sensor 133 may be mounted to thecenter pivot structure 102 to assist in determining the rotationalposition of the main section assembly 104.

In an implementation, the control device 130 is mounted to the centralpivot structure 102, a control cart, or a tower structure 110, 111, 112.The control device 130 is generally located on the structural element ofthe irrigation system 100 where the applicant/water is introduced intothe irrigation system; however, other configurations known in the artare within the scope of the present disclosure.

The control device 130 is configured to monitor operating conditions andconfigured to control various functions of the irrigation system 100. Incertain implementations, the control device 130 actively monitors theirrigation system's 100 function and performance including, but notlimited to: a position of one or more conduit sections 120, 121, 122 ortower structures 110, 111, 112 (e.g., the position of the main sectionassembly 104), whether the irrigation system 100 is powered on or off, avoltage parameter associated with the irrigation system 100, a motorspeed parameter associated with the irrigation system 100, anapproximate ground speed parameter associated with the irrigation system100, a direction parameter associated with the irrigation system 100, adiagnostic parameter associated with the irrigation system 100, whetherthe applicant is being supplied to the irrigation system 100 (e.g.,whether the fluid displacement device is operational), whether the Stopin Slot (SIS) is powered on or off, an applicant pressure associatedwith the irrigation system 100, a time parameter, a date parameter, afield position parameter of the irrigation system components, end-gunstatus, and whether the programs (e.g., software programs, etc.) arerunning properly. The control device 130 also controls the irrigationsystem's 100 functions and settings including, but not limited to: startand stop, selectively powering the main fluid displacement device, anapplicant application depth parameter, the direction of travelassociated with the irrigation system 100, selectively powering the SIS,automatically reversing or stopping the irrigation system 100,automatically restarting the irrigation system 100, providing anoperator auxiliary control to the system 100, writing and editingirrigation programs (e.g., irrigation software programs), andcontrolling sector and sequential programs (e.g., software programs). Inanother implementation, the control device 130 may cause an alert to beissued to the operator if there are any errors in the operation of theirrigation system 100 or if any of the functions or conditions monitoredby the control device 130 have been compromised (e.g., ceased operationor are outside an acceptable range).

The control device 130 may be housed in a weather-proof box and, asshown in FIG. 1B, includes at least a memory 134 to store one or moresoftware programs (e.g., software modules), a processor 136communicatively coupled to the memory 134, a user interface 138 (e.g.,graphical user interface, etc.), and a communications module 140 (e.g.,transmitter, receiver, transceiver, etc.). The memory 134 is an exampleof tangible computer-readable media that provides storage functionalityto store various data associated with the operation of the controldevice 130, such as software programs/modules and code segmentsmentioned herein, or other data to instruct the processor 136 to performthe steps described herein.

As described above, the irrigation system may include a plurality ofdrive units 118 mounted to each tower structure 110, 111, 112. As shownin FIG. 1C, each drive unit 118 may comprise a switched reluctance motor(SRM) 142. The switched reluctance motor 142 is an electric motorconfigured to operate utilizing reluctance torque. The use of switchedreluctance motors 142 allows for continuous speed adjustment (ascompared to motors not utilizing switched reluctance configurations),which allows for dynamic (“on-the-fly”) alignment adjustments of thespans 106, 108, 109. Additionally, the switched reluctance motors 142allow for the constant movement of the center pivot irrigation systems(as compared to center pivot irrigation systems not having switchedreluctance motors), which may allow for greater uniform application ofwater and/or chemicals while lessening waste.

As shown in FIG. 1C, the variable-drive units 118 may each include avariable-drive control unit 143. As shown in FIG. 1D, the variable-drivecontrol unit 143 includes a processor 202 is configured to provideprocessing functionality to the variable-drive control unit 143. Thus,the processor 202 may execute one or more software programs and/orinstructions described herein. The variable-drive control unit 143 alsoincludes a memory 204, which is an example of tangible computer-readablemedia that provides storage functionality to store various dataassociated with the operation of the variable-drive control unit 143,such as software programs/modules and code segments mentioned herein, orother data to instruct the processor 202 to perform the steps describedherein. In an implementation, the variable-drive control unit 143 isdirectly connected with the respective sensor 144 (e.g., via a wiredconnection). In this implementation, the variable control unit 143 isalso directly connected to the respective switched reluctance motor 142(e.g., via a wired connection). In another implementation, thevariable-drive control unit 143 may include a communication module 206,which is configured to communicate with other components (e.g., switchedreluctance motors 142, sensors 144) over a communication network (e.g.,a wireless network, a wired network, etc.). For example, thecommunication module 206 may be directed coupled (e.g., via one or morewires, or the like) to a corresponding variable-drive unit 118, as wellas a corresponding sensor 144. The communication module 206 may berepresentative of a variety of communication components andfunctionality, including, but not limited to: one or more antennas, atransmitter and/or receiver, a transceiver, or the like. While FIG. 1Dillustrates that the variable-drive control unit 143 is integrated(e.g., housed within) with the variable-drive unit 118, it is understoodthat the variable-drive control unit 143 may be a standalone unit.

As shown in FIG. 1C, each of the sensors 144 is in communication withthe respective variable-drive control unit 143. In a specificimplementation, the sensors are in direct electronic communication withthe corresponding variable-drive control unit 143. Previously,irrigation systems may have employed rod-and-switch actuators. Theseactuators may be replaced with the sensors 144 configured to monitor(e.g., determine) the span-to-span alignment of the irrigation system100. For example, the sensors 144 are configured to determine an anglebetween the corresponding spans. In one or more implementations, thesensors 144 may be potentiometers, captive alignment sensors, laserbased alignment sensors, non-contact proximity sensors, or other devicescapable of quantifiably measuring the span alignment (e.g., determiningan angle value between the corresponding spans) rather than merelydetermining if the respective span 106, 108, 109 is out of alignmentbeyond a preset maximum value. As described above, the sensors 144(potentiometers, the captive alignment sensors, the laser basedalignment sensors, and/or the non-contact proximity sensors) are inelectronic communication with the variable-drive control unit 143. Inresponse, the variable-drive control unit 143 is configured to furnish(e.g., provide, generate, transmit) one or more drive unit signals tocontrol the switched reluctance motor 142. For example, the processor202 of the variable-drive control unit 143 is configured to translatethe angle information furnished by the sensor 144 into speed informationthat is utilized to control the switched reluctance motor 142 (e.g.,control the speed of the corresponding span 106, 108, 109). Thus, thevariable-drive control unit 143 may furnish one or more drive unitsignals that are configured to cause a specified drive unit 118 tomodify the speed (e.g., increase the speed, decrease the speed) of theunit 118 (e.g., switched reluctance motor 142), which causes thecorresponding span 106, 108, 109 to vary in speed. In an implementation,the control device 130 may be configured to communicate with eachvariable-drive control unit during operation of the irrigation system100. For example, the variable-drive control unit 143 may be configuredto furnish diagnostic and/or performance information regarding thevariable-drive unit 118 to the control device 130.

In an implementation, a sensor 144 is configured to continually monitor(determine) the alignment values (e.g., angles) of the correspondingspans 106, 108, 109. In turn, the variable-drive control unit 143 isconfigured to furnish a drive unit signal configured to cause thecorresponding drive unit 118 to continuously modify the speed of thedrive unit 118 (e.g., modify the speed of the switched reluctance motor142) to re-align the corresponding mis-aligned span 106, 108, 109. Thus,the variable-drive control unit 143 is configured to continuouslyprovide signals, based upon the sensor 144 signal, to cause at leastsubstantially near-perfect (e.g., near-horizontal alignment) between thecorresponding spans by way of the switched-reluctance motors 142. Forexample, the speed of the drive unit 118 may be varied (via one or moredrive unit signals) based upon a deviation from a zero degree (0° spanto span alignment). In one or more implementations, the irrigationsystem 100 (e.g., sensors 144, variable-drive control unit 143, etc.)may utilize one or more motor control techniques to adjust the speed ofthe drive units 118 and/or measure the alignment of a particular span.For example, the irrigation system 100 may utilize aproportional-integral-derivative control algorithm, or the like, to finetune the speed of a particular drive unit 118. The variable-drivecontrol unit 143 is configured to continuously furnish one or more driveunit signals to the drive units 118 when the sensor 144 determines thata particular span is mis-aligned.

Thus, in operation, drive unit (control) signals configured to adjustthe set speed of a particular drive unit 118 are furnished to theparticular drive unit 118, which causes a drive unit speed adjustment.As described above, the drive unit signals may be based on potentiometersignals, captive alignment sensor signals, laser based alignment sensorsignals, non-contact proximity sensor signals, and/or other parametersuseful in determining a new set speed for a particular drive unit. Asdescribed above, the variable-drive control unit 143 includes aprocessor 202 that is configured to receive and to utilize data(information) from the tower structures 110, 111, 112 in determining theset speed for a particular drive unit 118. In an implementation, theprocessor 202 may comprise a microcontroller that includes dedicatedlogic (e.g., circuitry) for controlling the variable-drive units 118and/or the switched reluctance motors 142. For example, thevariable-drive control unit 143 may be in communication with each of thetower structures 110, 111, 112 by way of sensors 144, or the like. Asdescribed above, this may allow for finer speed control and dynamicalignment correction of the irrigation system 100.

CONCLUSION

Although the subject matter has been described in language specific tostructural features and/or process operations, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. An irrigation system comprising: a plurality ofinterconnected spans; a plurality of tower structures for supporting theinterconnected spans, each one of the plurality of tower structuresincluding a variable-speed drive unit for selectively driving a towerstructure at a selected speed; a plurality of sensors, each one of theplurality of sensors associated with a corresponding one of theplurality of interconnected spans and configured to determine analignment of a corresponding one of the plurality of interconnectedspans; and a plurality of variable-drive control units, eachvariable-drive control unit of the plurality of drive control units incommunication with a corresponding variable-speed drive unit and acorresponding sensor, each variable-drive control unit configured tocontrol the selected speed of the corresponding variable-speed driveunit to maintain the plurality of interconnected spans in asubstantially linear orientation with respect to adjacent ones of theplurality of interconnected spans along a generally longitudinallyoriented axis, wherein the selected speed of the correspondingvariable-drive control unit is based upon the alignment.
 2. Theirrigation system as recited in claim 1, wherein at least one sensor isconfigured to determine an angle between a first correspondinginterconnected span of the plurality of interconnected spans and asecond corresponding interconnected span of the plurality ofinterconnected spans; wherein the corresponding variable-drive controlunit is configured to determine a selected speed to maintain theplurality of interconnected spans in a substantially linear orientationwith respect to adjacent ones of the plurality of interconnected spansalong a generally longitudinally oriented axis, the selected speed basedupon the angle.
 3. The irrigation system as recited in claim 1, whereineach sensor of the plurality of sensors is in direct communication witha corresponding variable-drive control unit of the plurality ofvariable-drive control units.
 4. The irrigation system as recited inclaim 1, wherein the variable-speed drive units comprise switchedreluctance motors.
 5. The irrigation system as recited in claim 1,wherein the plurality of sensors comprise at least one of apotentiometer, a captive alignment sensor, a laser based alignmentsensor, or a non-contact proximity sensor.
 6. The irrigation system asrecited in claim 1, wherein at least one sensor of the plurality ofsensors is configured to continuously furnish a signal to thecorresponding variable-drive control unit, wherein the variable-drivecontrol unit is configured to continuously furnish a signal to avariable-drive unit of the corresponding interconnected span tocontinuously modify a speed of the corresponding tower structure tore-align the corresponding tower structure with the adjacent towerstructure.
 7. An irrigation system comprising: a center pivot structure;a main section assembly coupled to the center pivot structure, the mainsection assembly including a plurality of interconnected spans; aplurality of tower structures for supporting the interconnected spans,each one of the plurality of tower structures including a variable-speeddrive unit for selectively driving a tower structure at a selectedspeed; a plurality of sensors, each one of the plurality of sensorsassociated with a corresponding one of the plurality of interconnectedspans and configured to determine an alignment of a corresponding one ofthe plurality of interconnected spans; a plurality of variable-drivecontrol units, each variable-drive control unit of the plurality ofdrive control units in communication with a corresponding variable-speeddrive unit and a corresponding sensor, each variable-drive control unitconfigured to control the selected speed of the correspondingvariable-speed drive unit to maintain the plurality of interconnectedspans in a substantially linear orientation with respect to adjacentones of the plurality of interconnected spans along a generallylongitudinally oriented axis, wherein the selected speed of thecorresponding variable-drive control unit is based upon the alignment.8. The irrigation system as recited in claim 7, wherein at least onesensor is configured to determine an angle between a first correspondinginterconnected span of the plurality of interconnected spans and asecond corresponding interconnected span of the plurality ofinterconnected spans; wherein the corresponding variable-drive controlunit is configured to determine a selected speed to maintain theplurality of interconnected spans in a substantially linear orientationwith respect to adjacent ones of the plurality of interconnected spansalong a generally longitudinally oriented axis, the selected speed basedupon the angle.
 9. The irrigation system as recited in claim 7, whereineach sensor of the plurality of sensors is in direct communication witha corresponding variable-drive control unit of the plurality ofvariable-drive control units.
 10. The irrigation system as recited inclaim 7, wherein the variable-speed drive units comprise switchedreluctance motors.
 11. The irrigation system as recited in claim 7,wherein the plurality of sensors comprise at least one of apotentiometer, a captive alignment sensor, a laser based alignmentsensor, or a non-contact proximity sensor.
 12. The irrigation system asrecited in claim 7, wherein at least one sensor of the plurality ofsensors is configured to continuously furnish a signal to thecorresponding variable-drive control unit, wherein the variable-drivecontrol unit is configured to continuously furnish a signal to avariable-drive unit of the corresponding interconnected span tocontinuously modify a speed of the corresponding tower structure tore-align the corresponding tower structure with the adjacent towerstructure.
 13. An irrigation system comprising: a center pivotstructure; a main section assembly coupled to the center pivotstructure, the main section assembly including a plurality ofinterconnected spans; a plurality of tower structures for supporting theinterconnected spans, each one of the plurality of tower structuresincluding a switched reluctance motor for selectively driving a towerstructure at a selected speed; a plurality of sensors, each one of theplurality of sensors associated with a corresponding one of theplurality of interconnected spans and configured to determine analignment of a corresponding one of the plurality of interconnectedspans; a plurality of variable-drive control units, each variable-drivecontrol unit of the plurality of drive control units in communicationwith a corresponding variable-speed drive unit and a correspondingsensor, each variable-drive control unit configured to control theselected speed of the corresponding switched reluctance motor tomaintain the plurality of interconnected spans in a substantially linearorientation with respect to adjacent ones of the plurality ofinterconnected spans along a generally longitudinally oriented axis,wherein the selected speed of the corresponding variable-drive controlunit is based upon the alignment.
 14. The irrigation system as recitedin claim 13, wherein at least one sensor is configured to determine anangle between a first corresponding interconnected span of the pluralityof interconnected spans and a second corresponding interconnected spanof the plurality of interconnected spans; wherein the correspondingvariable-drive control unit is configured to determine a selected speedto maintain the plurality of interconnected spans in a substantiallylinear orientation with respect to adjacent ones of the plurality ofinterconnected spans along a generally longitudinally oriented axis, theselected speed based upon the angle.
 15. The irrigation system asrecited in claim 13, wherein each sensor of the plurality of sensors isin direct communication with a corresponding variable-drive control unitof the plurality of variable-drive control units.
 16. The irrigationsystem as recited in claim 13, wherein the plurality of sensors compriseat least one of a potentiometer, a captive alignment sensor, a laserbased alignment sensor, or a non-contact proximity sensor.
 17. Theirrigation system as recited in claim 15, wherein at least one sensor ofthe plurality of sensors is configured to continuously furnish a signalto the corresponding variable-drive control unit, wherein thevariable-drive control unit is configured to continuously furnish asignal to a variable-drive unit of the corresponding interconnected spanto continuously modify a speed of the corresponding tower structure tore-align the corresponding tower structure with the adjacent towerstructure.